Reliability-guided phase unwrapping algorithm: a review

Phase unwrapping algorithm plays very important role in noncontract optical profilometry, because the phase map acquired derectly is limited from pi to -pi, which is called wrapped phase. It must be unwrapped to retrieve the nature phase employing suitable phase unwrapping algorithm. In this paper, we review a phase unwrapping algorithm based on the reliability-guided parameter map. In this algorithm we select a parameter or group of parameters to identify the reliability of the phase data or the direction of phase unwrapping. The path of phase unwrapping is guided according to the parameter map. It means that the pixel with higher parameter value in the parameter map will be phase unwrapped earlier. The intensity modulation and the spatial frequency of the fringe pattern are usually used as important parameters characterizing the reliability. Other parameters, such as the phase difference between neighboring pixels, the signal-to-noise ratio, or some band elimination filter center around defect region assigned by user, could be selected as the optimized parameter for phase unwrapping. Sometimes we can combine two or three parameters to produce a more optimized parameter map for phase unwrapping. The advantage of this approach is that the path of phase unwrapping is always along the direction from the pixel with higher reliability value to the pixel with low reliability value. Therefore, in the worse case the error is limited, if there is any, to local minimum areas. (C) 2003 Elsevier Ltd. All rights reserved.